A. Field of the Invention
The present invention relates to a drum unit and a ground plate for image forming devices such as copying machines, facsimile devices or laser printers.
B. Description of Related Art
In an image forming device such as a copying machine, an image from an original document is optically read by an exposure unit, and a electrostatic latent image is formed on a photosensitive drum. A developing device is disposed adjacent to the photosensitive drum for forming a toner image thereon. The developing device includes a toner hopper, and toner supplied from the hopper is given an electric charge opposite that of the electrostatic latent image formed on the photosensitive drum. The toner adheres to the surface of the photosensitive drum to form a toner-developed image.
The photosensitive drum includes a tubular member formed from an electroconductive metal, and two flange members which are pressed into the openings defined on the opposite ends of the tubular member. An aperture is defined in the central portion of each of the flange members, and a support axle passages through the two apertures for supporting the drum-unit in the copying machine.
In order for electricity to flow between the surface of the tubular member and the body of the copying machine, a ground plate is attached to the flange member, with a portion of the outer circumference thereof in contact with a portion of the inner circumferential surface of the tubular member and the inner circumference thereof in contact with the support axle. However, because the inner surface of the tubular member is often coated with a substance for corrosion prevention, (such as aluminum oxide), this coating must be removed so that electricity can be conducted between the tubular member and the ground plate.
In order to do this portions of the ground plate have a diameter which are larger than the inner diameter of the tubular member. The ground plate is then forced into the tubular member, thereby deforming portions of the outer circumference of the, ground plate so that it may fit into the tubular member. This action scratches the inner circumferential surface of the tubular member, and removes enough of the coating so that electricity may be conducted between the tubular member and the ground plate.
However, due to the configuration of the ground plate, the tubular member can be deformed when the ground plate is forced into the tubular member. If the tubular member is deformed in such a manner, it may produce unsatisfactory copies. In addition, the tubular member is often made thinner in order to reduce the total weight of the copying machine, as well as its cost of production. However, the amount of deformation that occurs during ground plate installation often increases when the thickness of the tubular member is reduced.